Dynamoelectric machine



March 29, 1949.

C. A. THOMAS I DYNAMOELECTRIC MACHINE Filed Feb. 17, 1948 M w rm n 00 Ph 0 WT; V A ma .5

av C Patented Mar. 29, 1949 DYNAMOELECTRIC MACHINE Charles A. Thomas,Fort Wayne, Ind., assignorto General Electric Company, a corporation ofNew York Application February 17, 1948, Serial No. 8,783

16 Claims.

invention relates to dynamoelectric machines and more particularly tosuch machines of the commutator type having stator members provided withsalient main poles and interpoles.

In the design of commutator-type dynamoel'ectric machines, particularlyin the fractional horsepower frame sizes, it is necessary for maximumefliciency to effect substantial neutralization of the armature reactionat the point of commutation while providing a machine of minimumphysical size. Conventional interpoles may be utilized forneutralization of the armature reaction, however, the interpole windingsmay necessitate an undesirable increase in the overall size of themachine. Furthermore, in the design of commutator-type universal motors,the neutralization of armature reaction becomes of par ticularimportance and it is also frequently desirable to provide such a motorwith reversible characteristics.

An object of this invention is to provide an improved commutator-typedynamoelectric machine.

' Another object of this invention is to provide an improvedcommutator-type dynamoelectric machine of minimum size wherein thearmature reaction is overcome to secure proper commutation.

A further object of this invention is to provide an improved universalmotor of the commutator type in which the armature reaction is overcometo secure proper commutation.

tion will become apparent and the invention will i be better understoodby reference to the following description and accompanying drawing. The

features of novelty which characterize this in- 4 vention will bepointed out with particularity in the claims annexed to and forming apart of this specification.

A feature of this invention is the provision of a stator member for adynamoelectric machine having, for instance in a two pole machine, onlyone field coil on one salient pole, which provides flux for a consequentmain pole and a consequent interpole. This feature eliminates one fieldcoil and the interpole coil thereby eliminating the necessity ofproviding winding space and pole tips on the unwound poles. With thisconstruction, the advantages of the use of interpoles may be extended tomachines of minimum size where conventional interpol windings could notbe used. Furthermore, a reversible motor of minimum size may be providedby utilizing a field winding on each main pole, one for each directionof rotation, since the consequent interpole, as will be hereinafterpointed out, will functionproperly in either direction of rotation. Inaddition, the advantages of interpole armature reaction compensation canbe extended to universal commutator type motors where the resistance andreactance of interpole windings would normally be detrimental to theoutput of the machine.

In the drawing, Fig. 1 illustrates schematically a two poledynamoelectric machine of the commutator type provided with the improvedconsequent interpole construction of this invention, Fig. 2 illustratesa split series two-pole dynamoelectric machine constructed in accordancewith this invention, Fig. 3 shows the consequent interpole featureapplied to a two-pole dynamoelectric machine provided with amagnetically split stator construction, Fig. 4 shows a dynamoelectriemachine similar to Fig. 3 provided with a split series fieldarrangement, and Fig. 5 shows a stationary member for a commutator-typedynamoelectric machine constructed in accordance with this invention.

Referring now to Fig. 1, there is shown a twopole dynamoelectric machineprovided with relatively rotatable stator and armature members generallydesignated as l and 2 respectively. The stator member is formed of asubstantially cylindricai yoke portion 3 which may be convenientlyformed of a plurality of relatively thin laminations of magneticmaterial, or may be alter- 'applicationdesird. Theiyol re portion 3isprovided with-a "polar rajeenanerselient pole 4 extending radiallyinward therefrom, which is adapted to receive a field exciting winding.A second polar projection 5 is provided diametrically opposite from thepole 4 extending radially inward from the yoke portion 3. The pole faces6 and 1 respectively of poles 4 and 5 define a central bore in which isrotatably supported the armature member 2. The armature, which may be ofconventional construction, is provided with a commutator 8 which iscontacted by contact brushes 9 and It. A field exciting coil H ispositioned on the' pole 4 and is shown here connected in a seriesarrangement with the brushes and II to an external source of excitingpower I! and I3.

In order to provide the improved armature reis moved to contact 22 forthe other direction of action compensating feature of this invention,

and thereby insure proper commutation, the arrangement now to bedescribed is provided. A third polar projection 14 extends radiallyinward irom the yoke 3 and is positioned between the poles 4 and 5. Thefield exciting coil II is provided with sufilcient turns to .iurnish thenecessary operating excitation fiux and also to furnish sufilcientadditional commutation fiux to the interpole l4, the proper amount orcommutation iluxbeingregulatedbytheairgaplicithe interpole.

Assuming that themachine of. Fig. 1 is arrangedasamotorandthatthearma'tureis turning in the counter-clockwise direction asindicated, the operating flux iumished by the coil II will issue fromthe pole 4, traverse the armature and pole i, and return to pole 4through the yoke 3, as indicated by the arrows It. The armature reactionfiux caused by the current flowing in the armature conductors will thenhave a direction indicated by the arrow II. The provision oi theinterpole i4 will cause a portion of the fiux produced by the field coilii to be diverted and to cross the airgap l5 and enter the interpolereturning to the pole 4 through yoke I. This diverted fiux, indicated bythe arrow It, is in a direction opposite to the armature reaction fiuxII and can be made to substantially neutralize the It can now be readilyunderstood that the construction described above can be used toadvantage where it is desired to provide a'reversible split series motorwith good commutation. Reierring now to Fig. 2 wherein like parts aredesignated by like members, such an arrangement ape plied to a two-polemotor is shown. Here, the

stator i is provided with a substantiallycylindrical yoke portion 3 fromwhich polar projections 4 and 5 project radially inward. The yoke andpolar projections may be conveniently formed of laminated magneticmaterial, or may be of solid construction. The polar projections may beformed integral withthe yoke 3, or may beseparate parts secured in anyof the methods well known in the art. The pole faces 8 and 1 respec-.tively define the central bore in which is rotatably supported thearmature member 2 provided with commutator 8 and contact brushes I andI4. The polar projection 4 is again provided with a field excitingwinding Ii and in addition, the polar projection 5 is provided withfield exciting winding I. These windings are adapted to be excited fromthe external source 12 and II and switching means 20 is used toselectively energize either winding H or is depending upon the directionof rotation desired. As can be seen. the windings I i and is arearranged in series respectively with the brushes 8 and I0. Therefore,when the switch 20 is moved to contact 2|, winding ll only is energizedand, since the winding is is not energized, pole 5 becomes a consequentpole with respect to pole 4. Conversely, when the switch 24 rotation,winding ll only is energized and pole 4 becomes a consequent pole withrespect to p le I.

As in the embodiment oi Pig. 1', interpole i4 extends radially inwardfrom the yoke 8 between the poles 4 and 4 and forms an air gap II withthe armature 2. Assuming a counterclockwise direction of rotation oi thearmature with the field winding ll energised, the operating ilux willfollow the path indicated by the arrows II and the fiux diverted to theinterpole l4, indicated by the arrows II, can be made to substantiallyneutralize the armature reaction fiux, indicated by the arrow II, tosecure proper commutation. Now assuming a clockwise direction orrotation, with the field winding l4 energised the operating fiux willfollow the path indicated by the arrows 28, the direction being reversedfrom the direction or the operating fiux when winding H is energized.However, since the current fiowing in the armature windings is in thesame direction regardless of which held winding is energized, thearmature reaction fiux II will still be in the same direction. It cannow be readily seen that with the field winding ll understood from theabove description that this construction provides a split seriesreversible motor with the advantages of interpole commutation without,however, the necessity for providing interpole windings,

Referring now to Fig. 3, there is shown a commutator type dynamoelectricmachine similar to Fig. 1, however, with the magnetic circuit splitalong the axis of the two main poles. Here, there are providedrelatively rotatable stator and rotor members generally identified as 15and 26 respectively. The stator member comprises a substantiallycylindrical yoke portion 21 and two radially inwardly extending polarprojections 28 A and 28. The magnetic circuit is split, as at 40,

along a diameter of the yoke 21 extending substantially through thecenter of the poles 28 and 29. Nonmagnetic material may be interposedbetween the two segments of the yoke and the segments may be suitablysecured together mechanically by any convenient non-magnetic means. Thearmature is provided with a commutator II and contact brushes 3! and II.A field winding 34 is positioned 'on the pole 28 and connected in serieswith the armature through brushes 32 and It to a source of externalpower it and it. An interpole ll projects radially inward from the yokebetween the poles 24 and 28 forming with the armature an air gap 88.

As inthe embodiment of Fig. 1, the operating flux furnished by thewinding 34 follows a path indicated by'the arrows 3i and 44 through thetwo segments 01' the magnetic circuit. A portion of the operating fiuxis diverted to the interpole 81, as indicated by the arrows 4|, and isinthe proper direction to permit substantial neutralization or thearmature reaction 42 at the pointoi commutation.

The split magnetic circuit of Fig. 3 is provided in order to effectfurther neutralization ot the armature reaction flux. .As can be readilyseen,

assess the splitting of themagnetic path along the of the poles 28and'29 does not materially affeet the reluctance of the magnetic pathfollowed by the operating flux, however, the reluctance of the path ofthe armature reaction flux through tips of the poles 28 and 24 isconsiderably increased thereby substantially reducing the effect of thearmature reaction. With this con-- structiona smaller number of tiu'nscan be used in the winding 34 since less interpole fiux 4| is needed.This split magnetic circuit feature is particularly applicable touniversal motors since the heating and resultant power. loss due tohysteresis losses in the pole tips caused by the alternations of thearmaturereaction fiux'is substantially reduced. In addition, the motorcan be operated with heavier flux since the flux density by virtue ofthe split construction is nearly uniform across the pole face.

As in the case of the embodiment of Fig. 1, the split magneticconstruction with the consequent interpole is readily adaptable for useas a split series motor. Referring now'to Fig. 4, there is shown a splitseries two-pole motor substantially similar to the embodiment of Fig. 2,however, provided with the split magnetic feature of Fig. 3. Here, likeparts being indicated by like numbers, the stator member 25 comprises ayoke portion 21 and two radially inwardly extending polar projectionsand 28. The armature 26 has a commutator 3| which is contacted bybrushes 32- ,and 33. A field winding 34 is positioned on pole 28 andanother field windin .43

positioned on pole 29. The magnetic circuit is split, as at 30, along adiameter of the yoke extending substantially through the center of therespectively arranged in series with the armature through brushes 32 and33 and are excited from external source 35 and 36: A switch 44 is usedto select either winding 34 or 43 for the desired direction of rotation.Thus, when the switch 44 is at contact 45, winding 34 is excited and,since winding 43 is not excited, pole 29 forms a consequent pole withrespect to pole 28. Conversely, when the switch is at contact 46,winding 43 is energized and pole 28, forms a consequent pole withrespect to pole 29. As explained above under the discussion of Fig. 2,whichever field winding is selectively energized by the switch 44, aportion of the operating fiux will be diverted to the consequentinterpole 31 and, regardless of the direction of rotation, will be inthe correct direction to neutralize the armature reaction flux at thepoint of commutation. This construction permits the design'of areversible split series universal motor with the combined advantages ofsplit magnetic construction and interpole armathere is provided asubstantially cylindrical yoke 3 portion composed ofsegments 41 and 48.Pro- Jecting radially inward ,from the yoke segments are polarprojection segments 48 and 50 which pole tips define with the yokesegments 41 and 43 winding slots 53 and 54 respectively, adapted toreceive a field exciting winding. At a Point are provided with pole tipsBI and 52. These diametrically opposite from the polar projections 48and I0 is located a second set of polar projections 55 and 58 extendingradially inward from the yoke segments 41 and 48 respectively. The twostator segments may be separated by non-magnetic spacers 51 andappropriately secured together mechanically by conventional non-magneticmeans. A third polar projection 58 extends radially inward from the yokesegment 48 and is provided with a pole shoe 59. As, explained under thedescription of Figs. 1 through 4, this polar projection formsa'consequentinterpole and through the diversion of a portion of the fluxfurnished by the exciting winding, can be made to furnish a properamount of flux for good commutation, the armature reaction at the pointof commutation being overcome by flux from the field coil diverted tothe interpole. i A

Since only a single field exciting winding is provided, the polarprojections 55 and 56 form a consequent pole with poles SI and 52 andcan be of minimum size, no winding space being necessary. Thus,-the polefaces 60 and GI of the polar projections BI, 52 and 55, 56 respectively,together with the pole face 62 of the interpole 58, define-the centralbore, the centerline of which can be eccentric with respect to thecenterline of the yoke portion 41 and 48. This feature permitsconstruction of a machine with a much smaller distance from the mountingsurface to the rotor shaft. The eccentricity of the rotor shaft isparticularly applicable to gear motors. In such a motor with an outputshaft mounted for instance with the same eccentricity as the-rotorshaft, the gear inside the end shield can be madeto properly mesh withthe gear on the rotor shaft by simply rotating the end shield aboutthecenter of the yoke. Furthermore, due to the wide latitude in thedistance available between the center of the rotor shaft and the centerof the output shaft in such a construction, a wider range of gear ratioscan be made available than could be utilized with a'machine ofconventional construction.

While the embodiments described above are shown with series and splitseries field arrangements, it can be readily'understood that other fieldcircuits can be utilized with the improved construction of thisinvention.

From the foregoing it can be readily seen that the provision of aconsequent interpole provides a commutator-type dynamoelectric machineof minimum physical size yet with maximum efllciency due to the abilityto furnish proper flux for commutation without either extra commutatingwindings or by setting brushes at an angle from neutral.

While I have illustrated and described specific embodiments of thisinvention, modifications will occur to those skilled in the art and Iintend in the appended claims to cover all modi- 'fications which do notdepart from the spirit and scope of this invention. 1

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A stationary member for a commutator type motor or generator having acircular yoke portion, a polar projection extendingradially inward fromsaid'yoke adapted to receive a field coil for said dynamoelectricmachine, a second polar projection extending radially inward from saidyoke and forming a consequent pole with said first named polarprojection, and a single polar projection extending radially inward fromamass-i said yoke and interposed between said first and second namedpolar projections forming a consequent interpole with said first namedpolar projection. 2. A commutator type motor or generator havingrelatively rotatable armature and stator members; said stator membercomprising a circular yoke portion, apolar projection extending radiallyinward irom said yoke adapted to re- ,ceive a field winding for saiddynamoelectric first named polar projection, said single polarprojection iorming-a consequent interpole with said first named polarprojection whereby a portion of the fiux provided by said field coil isdiverted from said armature member into said single polar projectionsubstantially neutralizing the armature reaction in said armature at thepoint of commutation.

. ward from said yoke and positioned between said first named and secondnamed polar projections iorming a consequentinterpole with said firstnamed polar projection, said polar projections defining a central boreadapted to receive an armature member, the center line of said borebeing eccentric with respect to the center line of said yoke portion.

4. A commutator type motor or generator having relatively rotatablearmature and stator members; said stator member comprising, a circularyoke portion, a polar projection extending radially inward from saidyoke and adapted to receive a field coil for said dynamoelectricmachine, .a second polar projection extending radially inward from saidyoke and adapted to receive another field coil for said dynamoelectricmachine, and a. single polar projection extending radially inward fromsaid yoke and positioned between said first and second named polarprojections a field coil positioned on said first named polar projectionand adapted to be excited from an-external source, another field windingpositioned on said second polar projection and adapted to be excitedfrom said external source, and means for selecting either of said fieldcoils for .energization from said external source, the polar projectionassociated with the field coil not energized forming a consequent polewith the polar projection associated with the energized field coil, saidsingle polar projection forming a consequent interpole with the polarprojection associated with the energized field coil whereby a portion orthe flux provided by said field coil is diverted from said armature tosaid single polar projection substantially neutralizing the armaturereaction of said armature at the point 01' commutation.

for said dynamoelectric machine, a second polar projection extendingradially inward from said yoke and forming a consequent pole with said,

first named polar projection, and a single polar projection extendingradially inward from said yoke forming a consequent interpole with saidfirst named polar projection, said yoke and said first named and saidsecond named polar projections being split magnetically along a diameterof said yoke extending substantially through the centers of said firstnamed and second named polar projections.

6. A stationary member for a commutator type motor or generator having,a cylindrical yoke.

portion, a polar projection extending radially inward from said yoke andadapted to receive a field coil for said dynamoelectric machine, asecond polar projection extending radially inward from said yoke andforming a consequent pole with said first named polar projection. and asingle polar projection extending radially inward irom said a yokeforming a consequent interpole with said first named polar projection,said yoke and said first named and said second named polar projectionsbeing split magnetically along a diameter of said yoke extendingsubstantially through the centers of said first named and second namedpolar projections forming two yoke segments. and means for securing saidsegments together.

7. A stationary member for a dynamoelectric machine having, acylindrical yoke portion, a polar projection extending radially inwardfrom said yoke and adapted to receive a field coil for saiddynamoelectric machine, a second polar projection extending radiallyinward from said yoke and forming a consequent pole with said firstnamed polar projection, and another polar projectio'n extending radiallyinward from said yoke forming a consequent interpole with said firstnamed polar projection, said yoke and said first named and said secondnamed polar projections being split magnetically along a diameter ofsaid yoke extending substantially through the centers of said firstnamed and second named polar projections forming two yoke segments,nonmagnetic material interposed between said segments, and

5. A stationary member for a'commutator type means for securing saidsegments together.

8. A stationary member for a commutator type motor or generator having,a substantially circular yoke portion, a polarprojection extendingradially inward from said yoke adapted to receive I a field winding forsaid dynamoelectric machine,

a second polar projection extending radially inward from said yoke andforming a consequent pole with said first named polar projection, and asingle polar projection extending radially inward from said yoke andpositioned between said first named and second named polar projectionsforming a consequent interpole with said first named polar projection,said polar projections defining a central bore adapted to receive anarmature member, the center line of said bore being eccentric withrespect to the center line of said yoke, portion, said yoke portion andsaid first named and second named polar projections being splitmagnetically along a diameter oi said yoke extending substantially.through the center of said first named and said second named polarprojections. Q

9. A stationary member for a commutator type motor or generator having,a substantially circular yoke portion. a polar projection extendingradially inward from said yoke adapted to receive a field winding forsaid dynamoelectric machine, a second polar projection extendingradially'inwar from said yoke and forming a consequent pol with saidfirst named polar projection, a single polar projection extendingradially inward from said yoke and positioned between said first namedand second named polar projections forming a. consequent interpole withsaid first named polar projection, said polar projections defining acentral bore adapted to receive-an armature member, the center line oisaid bore being .eccentric with respect to the center line or said yokeportion, said yoke portion and said first named and second named polarprojections being split magnetically along a diameter of said yokeextending substantially through the center of said first named and saidsecond named polar projections forming twoyoke segments, and means fornonmagnetically securing said segments t ether.

10. A stationary member for 'a dynamoelectric machine having, asubstantially circular yoke portion, a polar projection extendingradially inward from said yoke adapted to receive a field winding forsaid dynamoelectric machine, a second polar projection extendingradially inward from said yoke and forming a consequent pole with saidfirst named polar projection, another polar projection extendingradially inward from said yoke and positioned between said first namedand second named polar projections forming a consequent interpole withsaid first named polar projection, said polar projections defining acentral bore adapted to receive an armature member, the center line orsaid bore being eccentric with respect to the center line of said yokeportion, said yoke portion and said first named and second named polarprojections being split magnetically along a diameter of said yokeextending substantially through the center of said first named and saidsecond named polar projections forming two yoke segments, nonmagneticmaterial interposed between said segments, and means for nonmagneticallysecuring said segments together.

11. A commutator type motor or generator having relatively rotatablearmature and stator members; said stator member comprising, a circularyoke portion, a polar projection extending radial- .iy inward from saidyoke and adapted to receive a field coil for said dynamoelectricmachine, a second polar projection extending radially inward from saidyoke and adapted to receive another field coil for said dynamoelectricmachine, and a single polar projection extending radially inward fromsaidyoke and positioned between said first and second named polarprojections; a field coil positioned on said first named polarprojection and adapted to be excited from an external source, anotherfield winding positioned on said second polar projection and adapted tobe excited from said external source, and means for selecting either ofsaid field coils for energization from said external source, the polarprojection associated with the field coil not energized forming aconsequent pole with the polar projection associated withthe energizedfield coil, said single polar projection forming a consequent interpolewith the polar projection associated with the energized field coilwhereby a portion 01' the fiux armature at the point of commutation,said yoke portionand said first named and said second named polarprojections being split magnetically along'a diameter of said yokeextending substantially through the center or said first named and saidsecond named polar projections.

12. A commutator type motor or generator having relatively rotatablearmature and stator members; said statormember comprising, a circularyoke portion, a polar projection extending radially inward from saidyoke and adapted to receive a field coil for said dynamoelectricmachine, a second polar projection extending radially inward from saidyoke and adapted to receive another field coil for, said dynamoelectricmachine, and a single polar projection extending radially inward fromsaid yoke and positioned between said first and second named polarprojections; a field coil positioned on said first named polarprojection and adapted to be excited from an external source, anotherfield winding positioned on said second polar projection and adapted tobe excited from said external source, means for selecting either of saidfield coils for energization from said external source, the polarprojection associated with the field coil not energized forming aconsequent pole with the polar projection associated with the energizedfield coil, said single polar projection forming a consequent interpolewith the polar projection associated with the energized field coilwhereby a portion of the fiux provided by said field coil is divertedfrom said armature to said single polar projection substantiallyneutralizing the armaturereaction of said armature a the point ofcommutation, said yoke portion an said first named and said second namedpolar projections being split magnetically along a diameter of said yokeextending substantially through the center oi said first named and saidsecond named polar projections forming two yoke segments, and means fornonmagnetically securing said segments together.

13. A dynamoelectric machine having relatively rotatable armature andstator members; said stator member comprising, a circular yoke portion,a polar projection extending radially inward from-said yoke and adaptedto receive a field coil for said dynamoelectric machine, a second polarprojection extending radially inward from said yoke and adapted toreceive another field coil for said dynamoelectric machine, and a thirdpolar projection extending radially inward from said yoke and positionedbetween said first and second named polar projections; a field coil p0-sitioned on said first named polar projection and adapted to be excitedfrom an external source, an-

other field winding positioned on said second polar projection andadapted to be excited from said external source, means for selectingeither of said field coils for energization from said external source,the polar projection associated with the field coil not energizedforming a consequent pole with the polar projection associated with theenergized field coil, said third named polar projection forming aconsequent interpole with the polar projection associated with theenergized field coil whereby a portion of the flux provided by saidfieldcoil is diverted from said armature to said third named polarprojection substantially neutralizing the armature reaction of saidarmature at the point of commutation, said yoke portion and said firstnamed and said second named polar projections being split magneticallyalong a diameter of said yoke extending substantially through thecenterof said first named and said second named polar projectionsforming two yoke segments, nonmagnetic, material interposed be tweensaid segments, and means for nonmagnetlcally securing said segmentstogether.-

v I I aeoaaaa radially inward from said yoke adapted to receive 5 afield winding for said dynamoelectric machine, a second polar projectionextending radially inward from said yoke and forming a consequent polewith said first named polar projection, and

a single polar projection extending radially in- 10 ward from said yokeand positioned between said first and second named polar projections;and a field coil positioned on said first named polar projection, saidsingle polar projection forming projection whereby a portion of the fiuxprovided by said field coil is divertedirom said armature member intosaid single polar projection substantially neutralizing the armaturereaction in said armature at the point or commutation, said yoke 2 15. Acommutator type motor or generator having relatively rotatable armatureand stator members; said stator member comprising a circular yokeportion, a polar projection extending radially inward from said yokeadapted to receive 0 a field winding for said dynamoelectric machine, asecond polar projection extending radially inward irom said yoke andforming a consequent pole with said first named polar projection, and

a single polar projection extending radially inward from said yoke andpositioned between said first and second named polar projections; afield coil positioned on said first named polar projection, -saidsinglepolar projection forming a consequent interpolewith s'aid first namedpolar projection whereby a portion of the fiux provided by said fieldcoil is diverted from said armature member into said last named polarprojection substantially neutralizing the armature reaction in saidarmature at the point or commutation, said 4 yoke portion and said firstnamed and said second named polar projections being magnetically splitalong a diameter of said yoke extending substantially through the centeror said first named and saidsecond named polar projections iorming twoyoke segments, and means for nonmagnetically securing said segmentstogether.

16. A dynamoelectric machine having relatively rotatable armature andstator members;- said stator member comprising a circular yoke portion,a polar projection extending radially inward from said yoke adapted toreceive a field winding .i'or said dynamoelectric machine, a secondpolar projection extending radially inwardfrom said yoke and .iorming aconsequent pole with said first named polar projection, and anotherpolar pma consequent interpole with said first named polar 15 jectionextending radially inward from said yoke and positioned between saidfirst and second named polar projections; a field coil positioned onsaid first namedpolar projection, said last named polar projectionforming a consequent interpole with said first named polar projectionwhereby a portion of the flux provided by said field coil is divertedfrom said armature member intosaid last named polar projectionsubstantially neutralizing the armature reaction in said armatur at thepoint of commutation, said yoke portion of said first named and saidsecond named polar projections being magnetically split along REFERENCESCITED The following references are of record in the file or this patent:

.UNITED STATES PATENTS Number Name Date 666,315 Johnson Jan. 22, 1901940,210 Steinmetz Nov. 16, 1909 1,255,607 Hensley Feb. 5, 1918 1,554,647Oswald Sept. 22, 1925 1,851,591 Parvin Mar. 29, 1932 Certificate ofCorrection Patent N 0. 2,465,824.

CHARLES A. THOMAS It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionas follows:

Column 12, line 26, claim 16, for the Words portion of read portion and;

and that the said Letters Patent should be read With this correctiontherein that the same may conform to the record of the casein the PatentOfiice.

Signed and sealed this 8th day of November, A. D. 1949.

THOMAS F. MURPHY,

March 29, 1949.

Certificate of Correction Patent No. 2,465,824. March 29, 1949.

CHARLES A. THOMAS It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionas follows:

Column 12, line 26, claim 16, for the Words portion of read portion and;

rrection therein that the same may conform to the record of the case inthe Patent Oflice.

Signed and sealed this 8th day of November, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

